Showing papers in "Journal of Macromolecular Science, Part B in 1980"

Polymer composites of rigid and flexible molecules: System of wholly aromatic and aliphatic polyamides

Abstract: As an extension of reinforcing principles of composite materials in which macroscopic fibers are dispersed in a ductile matrix, rigid microfibrils of wholly aromatic polyamides such as poly(p-phenylene terephthalamide) (PPTA), poly-p-benzamide (PBA), and their block copolymers with blocks of nylon 6 or nylon 66 were dispersed in a matrix of nylon 6 or nylon 66. On blending polyaramides with aliphatic polyamides, the spherulitic texture disappeared and a locally birefringent homogeneous texture was obtained. Electron microscopy revelaed that microfibrils of PPTA with diameter of 15-30 nm were dispersed in a fractured surface of the polymer composite. Strong interaction between the fibril surface and the matrix was suggested by the fact that the crystallization of matrix polyamides was induced by the rigid polyaramides. Wide-angle x-ray diffraction intensity curves, DSC curves of cooling process from the melt, and isothermal crystallization curves indicated a marked tendency for induced crystalliza...

Formation of interpolymer complexes

Abstract: Interpolymer complex formations of poly(methacrylic acid) (PMAA) or poly(acrylic acid) (PAA) with oligocations as well as poly(ethylene oxide) (PEO), and poly-(N-vinyl-2-pyrrolidone of various chain lengths were studied. For the case of complexation between PMAA and oligocations, the standard free energy change for the complexation ΔG° was found to be linearly dependent on the number of interacting sites, n. The stability constant K for complex is expressed as K = AeBnwhere A and B are constants which depend on the chemical structure of the polyelectrolytes. For the case of complex formation through hydrogen bonding, the degree of linkage Θ, defined as the ratio of the binding groups to the total of potentially interacting groups, and the stability constant K of the polymer-polymer complexes both in aqueous and aqueous-alcoholic media were determined as a function of temperature by means of potentiometric titration. It was found that Θ and K were strongly dependent on chain length, temperature, a...

Morphology-property relationships in polycarbonate-based blends. II. Tensile and impact strength

Abstract: The tensile and Izod impact strength of polycarbonate (PC) based polyethylene (PE) and polystyrene (PS) blends has been examined. The tensile strength can best be described as being proportional to an exponential function of the volume fraction of PE and the first power of volume fraction of PS. The variation of Izod impact strength with composition also differs considerably for the two blends, a small amount of PS causing a marked drop in impact strength. The impact strength of the PE/PC blend is related to the area under the tensile stress-strain curve, whereas for PS/PC blends no correspondence is found. The variation in properties is related to the composition, morphology, interfacial adhesion at the phase boundary and failure surfaces of the various blends.

Single crystals of poly(tetramethylene adipate)

Abstract: Single crystals of poly(tetramethylene adipate) (PTMA,-[O-(CH2)4-O-CO-(CH2)4-CO]n-) have been prepared by precipitation from solution and by epitaxial deposition on suitable substrates. The crystals grown from solution exhibited two distinct morphologies: most of the crystals were diamond-or truncated diamond-shaped, but a few were approximately hexagonal. These two morphologies yielded different diffraction patterns from which the polymorphic structures could be identified. Comparison of the electron diffraction patterns with the equatorial d spacings in the x-ray fiber diagrams indicated that the diamond and hexagonal morphologies correspond to β-and α-PTMA, respectively. The growth faces are the 110 planes for the β single crystals and both the 010 and 110 planes for the α single crystals. Epitaxial crystals were produced by deposition from the melt on trioxane and both from the melt and from solution on potassium halide crystals. The electron diffraction patterns of these crystals indicate th...

New morphologies in rubber-modified polymers

Abstract: New morphologies, especially “core-shell” and multilayered structures (“onion structure”) have been obtained for polymer blends containing block copolymers. For triblock copolymers Cop A-B-C, having three sequences of different types, in this case, poly(styrene-b-isoprene-b-methyl methacrylate), the conditions are given for the formation of core-shell structures. A scheme is presented showing the structures of the mesomorphic phases, as a function of the composition of the copolymer. Multilayered and core-shell structures have also been obtained by a suitable combination of two diblock copolymers, Cop A-B, i.e., poly(styrene-b-isoprene), with a corresponding homopolymer, i. e., polystyrene. One of the copolymers can act as an emulsifier for the second one forming the dispersed phase of the blend. An extension of the classical mesomorphic structures is presented, and it is shown that the emulsifying effect of block copolymers is quite general.

Morphology-property relationships in polycarbonate-based blends. I. Modulus

Abstract: The tensile, dynamic mechanical and morphological properties of PC/HDPE, PC/LDPE and PC/PS blends have been investigated with the intent of clarifying the major factors governing the modulus of these essentially incompatible blends. Scanning electron microscopy shows that all of the PC/HDPE, PC/LDPE and PC/PS blends have a domain structure whose morphology is strongly dependent on the concentration of the dispersed phase; when the dispersed phase concentration is less than 15%, the domains are mostly of spherical shape, while above 20% agglomeration takes place to form rodlike structures. Dynamic mechanical data shows there is essentially no adhesion at the PC-HDPE and PC-LDPE boundaries, while there is appreciable adhesion at the PC-PS interface. The existence of an intermixed zone was postulated to explain this interfacial adhesion. Morphological and thermal analysis results also indicate that both the HDPE and LDPE inclusions are loosely sitting in the holes in the PC matrix while the PS inclu...

Dynamics and thermodynamics of the liquid state (T < Tg) of amorphous polymers

Abstract: The liquid state behavior of the following atactic polymers has been reviewed: the alkyl and cycloalkyl methacrylates; polyisobutylene; polybutadiene, its random copolymers with styrene and acrylonitrile, and S-B diblocks; polystyrene; and the poly-α-olefins C3, C5, and C6. Just as Tg manifests itself through time-dependent (relaxational) and thermodynamic (transition) effects, so also does a T Tg or Tβ relaxation. With increasing syndiotactic content, PMMA's reveal strengthening Tβ and Tl processes. Relaxation maps plotting log frequency-T−1 are presented for PBD and PIB, showing both Tg and Tl. The latter exhibits non-Arrhenius behavior with an activation enthalpy about half that at T...

Multiple transitions in isotactic polypropylene around and above the glass transition

Abstract: Gas chromatography, thermal expansion, dynamic mechanical relaxation and thermally stimulated current measurements were used to study multiple transitions in isotactic polypropylene. The crystalline phase relaxation Tαc was decomposed into two components, Tαc1 and Tαc1, in order of decreasing temperature. The activation energy of the Tαc mode was found to be lower than that of the relaxation observed around the glass transition temperature. Thermally stimulated current (TSC) measurements revealed the existence of an apparent double liquid-liquid transition at 39°C and 68 °C in undrawn polypropylene and at 28°C and 55°C in drawn polypropylene. These TSC peaks correspond to a relaxation time following a Vogel equation whose critical temperatures let us predict an apparent double glass transition in polypropylene.

Mechanical properties of polymer mixtures: Effect of compatibility

Abstract: The effect of compatibility on the mechanical properties of polymer mixtures is discussed. From solution thermodynamics we conclude that for compatible mixtures of high molecular weight polymers the excess internal energy of mixing must be negative. For most polymer mixtures, this results in a negative excess volume of mixing. The excess entropy of mixing is therefore also negative. These general conclusions point to a stiffening of the solid lattice and a reduction in chain mobility. In dynamic mechanical behavior, the relaxation of molecular moieties responsible for the specific interaction should be shifted to intermediate temperatures, and the relaxation of other moieties should be shifted to higher temperatures if the potential well is inter-molecular. In finite deformation behavior craze initiation stress and shear yielding stress should both be higher than a linear combination of the properties of the pure components.

Morphology and properties of short segment block copolymers

Abstract: The structural, mechanical, and thermal properties of a polyetherpolyester segmented copolymer system [poly(tetramethylene oxide)/poly(tetramethylene terephthalate)] and two polycaprolactone-polyurethane elastomeric systems (based on 4, 4′-diphenylmethane diisocyanate or 4, 4′-dicylohexylmethane diisocyanate) were investigated. Experimental techniques employed in the analysis include DSC, dynamic mechanical testing, IR dichroism, small-angle x-ray and laser light scattering, and tensile testing. Results show that material properties can be explained in terms of system compatibility, crystallization characteristics, and domain morphologies.

Relaxation processes in the glassy state: Molecular aspects

Abstract: Molecular relaxations in the glassy state of amorphous polymers are discussed, and related to the energy requirements of the various possible molecular motions involved under two broad headings: those occurring in groups pendant to the main chain and those occurring in the main chain units themselves. A variety of motions can result in relaxations in polymers with alkane side chains, whereas only rotation (or partial rotation) is possible for pendant phenyl rings. Relaxations in polymers with cycloalkane rings in the side chain can originate within the ring itself or from motion of the ring as a unit. Restricted movements of various types of backbone chain are discussed, and possible alternatives to the postulated crank-shaft motions in polymethylene chains are presented.

Microdomain structure and some related properties of block copolymers. II. Plastic deformation mechanisms of the glassy component in rubber-toughened plastics

Abstract: The toughening mechanism was investigated by means of mechanical and optical techniques including electron microscopy and polarized light scattering for wide variety of domain morphologies of di-and triblock copolymers and their blends with corresponding homopolymers. Two types of plastic deformation mechanisms of glassy component are emphasized a s the toughening mechanism. One is large plastic deformation of the glassy component, a s bulk, followed by its plastic flow o r fragmentation, depending on the di-or triblock sequence arrangement. The other is development of a microcraze a t the boundary of the rubber particle and its propagation through the glassy matrix. The origins of the two types of plastic deformation mechanisms are postulated a s hydrostatic pressure effects upon the high plasticity of the glassy component due to differences of Poisson's ratios between the glassy and rubbery components and as stress concentration effects of the rubber particle at the glassy phase opposite to the...

Pressure-volume-temperature relationships of solid and molten poly(ethylene terephthalate)

Abstract: The pressure-volume-temperature (PVT) properties of poly(ethylene terephthalate) (PET) have been studied experimentally and theoretically in the temperature range 30–342 °C and at pressures to 2000 kg/cm2. In the semicrystalline solid state (ρ = 1.409 g/ cm3 at 20°C), two transitions were resolved. One is the glass transition at Tg = 70°C (P = 0), increasing with pressure according to dTg/dP = 0.025 °C/(kg/cm2). A second transition was observed as a break in the zero-pressure isobar and also as a break in the zero-pressure compressibility versus temperature curve at 160°C. It is interpreted as a premelting (αc) transition. The melt data were fitted successfully to both the empirical Tait equation and the Simha-Somcynsky hole theory (with T∗ = 11710°K, V∗ = 0.7408 cm3/g, and P∗ = 11570 kg/cm2). The Simha-Somcynsky theory was also used to establish a semi-empirical equation of state for amorphous PET in the temperature range Tg < T < Tm and to derive a theoretical pressure dependence of Tg in compl...

Anisotropic mechanical properties of drawn nylon 6. I. The α phase

Abstract: Cold-drawn uniplanar-axially oriented sheets of nylon 6 have been annealed at 195°C, hot-rolled at 130°C, and then chemically treated with phenol to form the α crystalline phase. The morphology is parallel-lamellar, with the molecular chains at right angles to the lamellar plane. The long period is 96.7 ± 0.7 A. The extensional compliances S33 (parallel to the draw direction) and S11 (the transverse direction in the sheet) and the shear compliances S44, S55, and S66 have been measured at 20.0 ± 0.3°C by dead-loading creep and torsional methods, in two relative humidity ranges, 0–10% and 61–69% RH. Dependence upon time (creep), strain, and humidity have also been determined. The extensional compliances show the cross-over of S33 above S11 when the αa transition or Tg is reduced to below room temperature by increasing the relative humidity from zero to 65%. The results are explained by using Takayanagi models for the extensional compliances and interlamellar shear or crystallite shear for the shear...

Composition and molecular weight distribution of block copolymers

Abstract: The composition distribution (CS) of diblock copolymers of styrene and methyl methacrylate, prepared anionically via a sequential addition procedure, has been investigated by two methods, one based on the theory of light scattering from copolymer solutions and the other on the principle of adsorption chromatography. Calculations were carried out to show that if the structure of the sample block copolymer is described by random coupling statistics, information of the molecular weight distribution (MWD) for either one of the block chains can be drawn from light scattering data obtained with one single solvent in which the solute is invisible. In practice, bromobenzene was used as a solvent appropriate for this purpose. Since the MWD for the precursor polystyrene is known, the MWD for the poly(methyl methacrylate) block was determined by this method. By using these data and assuming the Schulz distribution for MWD, the CD curve was calculated. Fractionation of the block copolymer sample by compositi...

Mixed crystals in polymer blends: Polypropylene-polybutene-1 system

Abstract: A method of preparing solid solutions of chemically different polymeric molecules in the crystalline state is reported. The characteristic feature of the method is the high longitudinal flow gradient in which one can achieve very high rates of crystallization as well as supercooling at constant temperature. In the present study, isotactic polypropylene-polybutene-1 blends of different compositions were investigated, and solid solutions were observed up to 20% on each side of the phase diagram. The resultant crystalline blends were investigated by using transmission electron microscopy (TEM) and electron diffraction, wide-angle x-ray diffraction, differential thermal analysis, and mechanical testing. Structural studies reveal the presence of needle-like crystals within the blends. The thermal stability of the blended crystals is unexpectedly high with no major changes in the structure upon annealing. The mechanical properties exhibit only small changes for the different blends.

Experimental aspects of compatible polymer mixtures

Abstract: Recent investigations on the possible applications of thermodynamic concepts to experimental studies of polymer mixtures by using the phase diagram are presented. Phase separation behavior may be classified into three categories, namely amorphous-amorphous polymer, crystalline-amorphous polymer, and crystalline-crystalline polymer mixtures. In the theoretical part of this paper, Scott's treatment of polymer mixtures based on the classical Flory-Huggins equations are used to calculate the spinodal, binodal, and melting point depressions. In the case of amorphous-amorphous polymer mixtures, phase diagrams were gathered from the literature. Lower critical solution temperature type phase diagrams for polystyrene-poly(vinyl methyl ether) were introduced and analyzed. As to the phase separation behavior, both spinodal decomposition and nucleation and growth mechanisms were observed. For crystalline-amorphous polymer systems, crystalline polymer melting point depressions were analyzed for a poly(vinylid...

Photon correlation spectroscopy of poly(ethyl methacrylate) near the glass transition

Abstract: Poly(ethyl methacrylate) has been studied by photon correlation spectroscopy in the temperature range 70–150°C. The relaxation function for longitudinal density fluctuations is highly nonexpon-ential and changes shape dramatically as the sample is cooled. The results indicate that there are multiple relaxation processes which have different apparent activation energies. The average relaxation time changes by a decade with a 5°C change in temperature near Tg. The breadth of the distribution of relaxation times near the glass transition is at least eight decades.

Effect of polymer molecular variables on drag reduction

Abstract: Drag reduction is the reduction in energy loss in turbulent flows caused by high polymer or other additives. Although the phenomenon was first observed independently by Mysels and by Toms over three decades ago, the complex interactions of the polymer molecules and the turbulent flow are still not well understood. This paper reviews some of the unusual flow characteristics of drag-reducing solutions, discusses potential applications, and points out the limitations posed by mechanical degradation. The effect of polymer molecular weight, molecular weight distribution, concentration, and solvency on drag reduction are shown for narrow molecular weight polystyrene samples and their mixtures. Various hypotheses for predicting the onset of drag reduction are discussed and compared with measured onset values. The data are best fit by a time-scale hypothesis which depends on the ratio of a molecular relaxation time to a characteristic time of the flow (Deborah number). Two measures of the relative effect...

Thermodynamics of the glassy state of polymers

Abstract: After a short discussion of the nature of the glass transition, a concept of ordering parameters is given which allows a thermodynamic treatment of the glass transition and the glassy state. PVT-measurements on atactic polystyrene show that the Ehrenfest equations which describe a thermodynamic transformation of the second order are not applicable to the glass transition. The introduction of one ordering parameter ζ in addition to the conventional variables T and P is sufficient to describe the behavior of PS in the glassy state nearly quantitatively. The Ehrenfest equations must be replaced by other equations which in the simplest case contain only one ζ parameter (freezing-in model). It will be shown that the nonvalidity of the Ehrenfest equations results in a path dependence of the thermodynamic properties in the glassy state. Recent PVT measurements on a polymer liquid crystal show that the physical properties in the nematic phase do not depend on the path and are not time-dependent. At lower...

Statistical Thermodynamics of Bulk and Surface Properties of Polymer Mixtures

Abstract: A generalized version of the lattice fluid theory of solutions is considered. Necessary and sufficient conditions for phase stability in a binary mixture are defined by a spinodal inequality. From the general properties of the spinodal, the necessary conditions for polymer/polymer miscibility and bimodal behavior of the spinodal are defined. A general theory of interfacial tension in phase separated multi-component mixtures is formulated. The interfacial tension theory can be combined with lattice fluid theory to obtain a unified theory of bulk and interfacial properties.

Dielectric study of polymer compatibility: Blends of polystyrene/poly-2-chlorostyrene

Abstract: The dielectric constant and loss have been monitored isothermally in the frequency plane in the α relaxation region for a series of amorphous compatible and phase separating polymer blends comprising one polar and one relatively non-polar component. Differential scanning calorimetry has been employed for preliminary assessment of the miscibility of a given pair. The system polystyrene/poly-2-chlorostyrene (PS/PoCS) has been found to exhibit miscibility highly dependent on molecular weight and temperature. High molecular weight blends display wide loss spectra; phase separation above a lower critical solution temperature (LCST) results in the narrowing of the loss curves. Low molecular weight polystyrene yields blends which remain homogeneous up to degradation temperatures and exhibit narrow loss peaks. Comparison between PS/PoCS blends and random copolymers of styrene and 2-chlorostyrene is made.

Dielectric properties and conductivity of styrene-methacrylic acid copolymers and partially neutralized salts

Abstract: Dielectric and conductivity measurements have been carried out on styrene-methacrylic acid copolymers and their salts in the glass transition region, stressing the comparison of polymers neutralized to different extents. A simple monomer-dimer equilibrium between carboxylic acid groups is applicable to the pure acid polymers, which explains the increase of both the glass transition temperature and of the dielectric strength with concentration of methacrylic acid. The dielectric data indicate that very few sodium carboxylate groups can dissolve in the matrix of the pure salt, whereas the presence of carboxylic acid groups in partly neutralized polymers enhances the dissolution of the salt groups in the matrix. Considerable differences are observed between the partly neutralized polymer and the blend consisting of pure acid and pure salt copolymers, which suggests that exchange of cations between acid and salt groups is quite slow even at high temperatures. The conductivity of the ionomers appears ...

Morphology-mechanical property relationship of a polystyrene-polybutadiene-polystyrene block copolymer and its blends with homopolymers

Abstract: The morphology-mechanical property relation was investigated on a polystyrene-polybutadiene-polystyrene (SBS) block copolymer and its blends with polystyrenes (PS) and polybutadienes (PB) cast from a THF/MEK mixture (T/M) and a cyclohexane/benzene mixture (C/B). As-cast films with alternating lamellar morphology such as SBS (T/M) always show high moduli and “plastic-torubber” transitions, while those with PS-dispersed-in-PB-matrix morphology always exhibit low moduli and crosslinked rubberlike behavior. All these systems undergo strain-induced softening, accompanying breakdown of glassy PS domains, and show rubberlike behavior, regardless of the sample prehistory. However, upon annealing under adequate conditions, all these softened systems eventually revert to their original morphology and behavior.

Transport and solution of gases and vapors in styrene-butadiene block copolymers: Absorption and desorption of n-hexane vapor

Abstract: The integral absorption and desorption of n-hexane vapor by styrene-butadiene block copolymers were studied as a function of film thickness and vapor pressure at 25°C by use of a weighing method. The morphologies of the samples were (1) polystyrene rods dispersed in a polybutadiene matrix and (2) a series of alternating lamellae of styrene and butadiene components. For both copolymer samples (1) and (2), reduced solvent weight uptake plots for films of differing thicknesses did not give a single curve ½ when plotted against the Fickian variable, t½/X, where t is time and × is film thickness, though the individual absorption and desorption curves appeared to have a Fickian shape. In certain concentration regions, the two-stage type of non-Fickian behavior was observed with copolymer film having a type (2) morphology. As expected, absorption and desorption processes in homopolybutadiene films were purely Fickian. From these results it was concluded that the segmental motions in the polybutadiene ph...

Corresponding states principle for newtonian viscosities-temperature effects

Abstract: In the first part of the paper a superposition method for the polymer solution zero shear rate viscosity ηo as a function of concentration c is reviewed. The method was successful in numerous systems, but it partially failed in four, the worst case being polyisobutene in isooctane, where data were available over the full concentration range and molecular weights (MW) ranged from 900 to 2.5 × 106. It was postulated that the possible cause for this is either MW dependence of Tg which would result in a faster than expected increase in ηo for higher MW samples, or a difference in flow mechanism between the solutions at low and high concentration. In the second part, a new theory for the temperature effect on ηo is proposed. The theory permits linearization of ηo (T) results both for small molecules and for polymeric liquids. In systems where a transition occurs, the linearized plot shows a sharp break. The theory was extended to the concentration dependence of the polymer solution viscosity. It permi...

Thermodynamics of mixed polymer melts

Abstract: The compatibility of polymer mixtures is discussed from a thermodynamic standpoint. Deviations from the simple lattice theory (Flory-Huggins) show up sensitively in phase diagrams. Possible molecular origins for such deviations are discussed. Experimental techniques that have recently been developed to deal with highly viscous mixtures are described.

Formation of polyelectrolyte complexes

Abstract: Interactions between polyelectrolytes carrying opposite charges in aqueous media may lead to either complex coacervation or the formation of interpolymer complexes, depending on the charge density and concentration of polymer components, ionic strength, temperature, and pH. The liquid-liquid phase separation referred to as complex coacervation was thought by Oparin to be an origin of prebiological systems. This article summarizes our recent results on the intermolecular interactions between charged polymer molecules, from the point of view of biological interests.

Modelling of the viscoelastic behavior of homogeneous and heterogeneous blends of polyisoprene and polybutadiene

Abstract: The mechanical model of Takayanagi has been used to describe the viscoelastic behavior of various blends of a ternary elastomer system (cis-1, 4 polyisoprene, 1, 4-polybutadiene, and the corresponding polyisoprene/polybutadiene diblock) for which extensive mechanical properties data have already been reported. Through the use of appropriate composition-temperature shifts which rely on the assumption of free volume additivity, it was possible to model the behavior of the homogeneous diblock copolymers of polyisoprene and polybutadiene as well as various homogeneous binary and ternary blends of a diblock with either or both of the diene homopolymers. Heterogeneous ternary blends were also modelled successfully by assuming that the diblock was solubilized preferentially by one of the phases in the blend. The model predictions were very sensitive to the location of the diblock, and thus comparison with experimental results provided a useful tool for verifying earlier assumptions regarding the role of...